A controller pilot data link communications (CPDLC) human machine interface (HMI) is a set of screens used by members of an aircraft flight crew to receive uplink messages from the air traffic controller and to send downlink messages to the air traffic controller. Today when a pilot of an aircraft wants to change altitude or speed, the pilot talks to the air traffic controller (ATC), typically, via a very high frequency (VHF) radio and asks for the desired altitude or speed. The ATC datalink system (also referred to herein as a CPDLC system) permits the pilot make the request for the desired altitude or speed via a datalink. The air traffic controller responds to the message containing the speed or altitude request via datalink.
Some downlink request messages receive a negative response message, such as a CPDLC uplink message UNABLE message, from the controller. The negative response message (also referred to herein as a “negative uplink response message”) is uplinked to the pilot, who reads the uplink message of UNABLE. For example, the air traffic controller sends an UNABLE or NEGATIVE message when air traffic in the vicinity of the aircraft would endanger the aircraft if the aircraft accelerated (or decelerated) to the requested speed or if the aircraft moved to the requested altitude. If the controller responds UNABLE, then the pilot may enquire “When can we expect . . . ”.
Currently, if the pilot wants to respond to the UNABLE message that is received from the controller, the pilot searches a message log for the downlink request message to which the UNABLE is responsive. After the pilot finds the associated downlink request message in the message log, the pilot navigates through the air traffic control (ATC) menu screens, and composes the “when can we expect . . . ” message by filling in the data to match the original downlink request message, and sends the “When can we expect . . . ” message. This process requires considerable “head-down time” during which the pilot is looking down at the display, which shows the CPDLC HMI screens, and is unable to focus on other aspects of flying the aircraft. If there is operational urgency in the message being sent, this head-down time adds time to the processing of the message and delays an urgently required action.